Bottom-supported marine structures are commonly installed at offshore locations for a variety of reasons, e.g. the drilling and production of hydrocarbons. Typically, one or support members (e.g. legs or piles) are embedded in the marine bottom and extend to above the water surface to support a drilling and/or production platform. It is also common to run flowlines, control lines, etc. (collectively called "risers") from the marine bottom to the surface along these support members. As is well known in the industry, these support members and the risers are subject to damage due to corrosion, erosion, collisions, etc. and are likely to require repair and/or replacement from time to time. This is especially true of those portions of the support members and risers which extend through the "splash zone", i.e. the zone of water at or near the surface which experiences the forces generated by the action of the waves.
The repair of these elements, especially in the splash zone, have proven costly due to the specially trained personnel and the excessive time normally required to perform the work. That is, often highly trained divers are required to work for long periods to carry out what would otherwise be a fairly routine operation. In other instances, a "cofferdam" or "habitat" has to be installed around the support member and riser to provide the proper environment for the personnel to work in.
As known in the art, a "cofferdam" is a watertight enclosure which is normally formed of sheet piles which are driven into the marine bottom and extend to above the water's surface. The sheets are connected to form a watertight enclosure around the support member and/or risers and is open to the atmosphere at its top. After the water is pumped out of the cofferdam, personnel can enter the enclosure and work in a relatively "dry" environment. While cofferdams provide a good work area, they are only practical in relatively shallow depths and they must be constructed and dismantled in their entirety each time they are used. Obviously, this is very expensive and time consuming.
"Habitats" are work enclosures which are not exposed to the atmosphere but instead are completely enclosed structures which are used below the surface. They usually consist of two sections which are bolted together and sealed around a member to be serviced. Once sealed, the habitat is pumped out and pressurized depending on the depth installed. The work performed in a habitat is carried out with divers with entrance being directly through the water or from a diving bell. Habitats are normally specifically designed for a particular application. Sometimes, however they can be reused but only after they undergo major fabrication modifications. Again, the use of these types of work enclosures, especially in the splash zone, is extremely expensive and time consuming.
Accordingly, a real need exists for a work enclosure which can be used over and over again with little or no modification and one which can be quickly installed and removed from a marine support member to provide a "dry" work area for personnel in the splash zone.